The present invention relates to a light emitting device using micro-crystals, a production method thereof, and a light emitting apparatus and a display unit using the light emitting device.
Light emitting devices using semiconductors such as GaAs, GaAsP mixed crystal, GaAlAs mixed crystal, and GaP have been developed. Such a light emitting device has a structure in which an n-type semiconductor layer, a light emitting layer, and a p-type semiconductor layer are sequentially stacked on a substrate. When a voltage bias is applied to the light emitting device in the forward direction, electrons are recombined with positive holes in the light emitting layer, to thereby generate light emission. In accordance with a related art production method, each of the n-type semiconductor layer, light emitting layer, and p-type semiconductor layer has been composed of a single crystal body formed on the substrate by epitaxial growth. Accordingly, the substrate has also been formed of a single crystal body.
In a method of producing such a related art light emitting device in which each of the n-type semiconductor layer, light emitting layer, and p-type semiconductor layer is composed of a single crystal body, the alignment in lattice or alignment in crystal structure between the layer and the substrate is essential to ensure a good crystallinity of the layer; and the epitaxial growth condition is severely limited and the epitaxial growth must be performed at a high temperature to reduce occurrence of defects, with a result that the kind of material for the substrate is significantly limited, that is, the degree of freedom in selection of the material for the substrate becomes small. Accordingly, the related art light emitting device causes a problem in which since quarts or glass cannot be used for a substrate, it is impossible to produce a device array formed on a common substrate having a large area.
The materials for forming the light emitting material, n-type semiconductor layer, and p-type semiconductor layer are also significantly limited by the material of the substrate, and the degree of freedom in selection of the materials for forming the above layers is small. This causes a problem that the wavelength of light emission is limited. Further, although various attempts have been made to reduce defects as described above, it is impossible to perfectly eliminate the defects. Since the remaining defects act as non-luminescence centers, there occurs a problem that the emission efficiency is reduced and the performance of the light emitting device is degraded.
An object of the present invention is to provide a light emitting device capable of enhancing the emission efficiency, extending the selection range of materials, and forming a device array on a common substrate having a large area; a production method thereof; and a light emitting apparatus and a display unit using the light emitting device.
To achieve the above object, according to a first aspect of the present invention, there is provided a light emitting device including: a first conductive type layer; a second conductive type layer; and a micro-crystal layer containing a plurality of micro-crystals made from a semiconductor, the micro-crystal layer being formed between the first conductive type layer and the second conductive type layer. With this configuration, since the micro-crystal layer is composed of a plurality of the micro-crystals with few defects, the crystallinity of the micro-crystal layer can be improved, to thereby enhance the emission efficiency and prolong the service life. Since it is not required to take into account the lattice alignment with the substrate, it is possible to select a suitable material in accordance with the desired emission wavelength and the like. Since the band gap of the micro-crystal layer becomes wider as the grain size of each micro-crystal becomes smaller by the particle size effect, it is possible to shorten the wavelength of light emission. For example, it is possible to obtain light emission in an ultraviolet region by using the micro-crystals made from ZnO. The light emitting device allowing light emission in the ultraviolet region can be used as a light source for a germicidal lamp. Further, since each of the first conductive type layer and the second conductive type layer is not required to be formed of a single crystal body, the selection range of the material for each of the layers can be extended, and since each of the first conductive type layer and the second conductive type layer can be formed of a non-single crystal body of an inorganic semiconductor, an organic semiconductor, or a conductive resin, it can be easily formed at a low temperature.
In the above light emitting device, the micro-crystal layer may contain two kinds or more of micro-crystals made from different semiconductors. With this configuration, there can be obtained an effect of obtaining a plurality of kinds of light emission having different wavelengths.
In the above light emitting device, the micro-crystal layer may contain micro-crystals each having a layer-structure. With this configuration, there can be obtained an effect of further enhancing the emission efficiency.
In the above light emitting device, at least one of the first conductive type layer and the second conductive type layer may be made from a non-single crystal body, or at least one of an organic semiconductor and a conductive resin. With this configuration, there can be obtained an effect of easily forming at least one of the first conductive type layer and the second conductive type layer at a low temperature.
In the above light emitting device, at least one of the first conductive type layer and the second conductive type layer may have a plurality of layers which are stacked in such a manner that a band gap of the conductive type layer becomes smaller at a portion nearer to the micro-crystal layer. With this configuration, there can be obtained an effect of further enhancing the emission efficiency.
In the above light emitting device, at least one of the first conductive type layer and the second conductive type layer may have an adhesive layer. With this configuration, there can be obtained an effect of enhancing the adhesiveness of an electrode.
In the above light emitting device, at least one of the first conductive type layer and the second conductive type layer may have an electrode layer. With this configuration, there can be obtained an effect of eliminating the need of newly forming an electrode made from a metal or a metal alloy, and thereby simplifying the device structure and the production steps.
In the above light emitting device, an insulating layer for preventing the contact between the first conductive type layer and the second conductive type layer may be formed in spaces between the micro-crystals of the micro-crystal layer. With this configuration, it is possible to reduce leakage current between the first conductive type layer and the second conductive type layer, accordingly electrons and positive holes can be efficiently injected in the micro-crystals. As a result, there can be obtained an effect of improving the emission efficiency.
In the above light emitting device, the substrate may be made from an amorphous material or a plastic material. With this configuration, there can be obtained an effect of easily enlarging the area of the substrate, thereby forming a device array on a common substrate having a large area.
In the above light emitting device, the substrate may be made from a metal, a semiconductor, or silicon carbide. With this configuration, there can be obtained an effect of uniformly applying a voltage over the entire micro-crystal layer, thereby uniformly generating light emission from the entire surface of the micro-crystal layer, and further simplifying the production steps. Also, there can be obtained an effect of easily enlarging the area of the substrate, thereby forming a device array on a common substrate having a large area.
In the above light emitting device, a diffusion preventive layer may be formed between the first conductive type layer and the second conductive type layer. With this configuration, there can be obtained an effect of preventing the diffusion of components between the substrate and the first conductive layer, thereby improving the quality of the light emitting device.
In the above light emitting device, an auxiliary electrode may be formed between the first conductive type layer and the substrate. With this configuration, there can be obtained an effect of uniformly applying a voltage over the entire micro-crystal layer, thereby uniformly generating light emission from the entire surface of the micro-crystal layer.
The above light emitting device may further include a phosphor layer. With this configuration, there can be obtained an effect of easily changing colors of light emission by changing phosphor materials for forming the phosphor layer, and hence to extend the selection range of the phosphor materials and extend the range of colors of light emission.
According to a second aspect of the present invention, there is provided a light emitting device including: a first conductive type cladding layer; a second conductive type cladding layer; and a light emitting layer containing a plurality of micro-crystals, the light emitting layer being formed between the first conductive type cladding layer and the second conductive type cladding layer. With this configuration, there can be obtained the same effects as the corresponding effects obtained by the light emitting device according to the first aspect of the present invention. Further, in this light emitting device, an insulating layer is provided between the first conductive type cladding layer and the second conductive type cladding layer. With this configuration, there can be obtained the same effects as the corresponding effects of the light emitting device according to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a method of producing a light emitting device, including the steps of: forming a first conductive type layer; forming a micro-crystal layer containing a plurality of micro-crystals made from a semiconductor on the first conductive type layer; and forming a second conductive type layer on the first conductive type layer via the micro-crystal layer. With this configuration, there can be obtained an effect of easily producing the light emitting device of the present invention, thereby easily realizing the light emitting device of the present invention.
In the above production method, the formation of a micro-crystal layer may be followed by a heating treatment in an oxygen containing atmosphere, a nitrogen containing atmosphere, or hydrogen containing atmosphere. With this configuration, there can be obtained an effect of improving the crystallinity of the micro-crystals.
In the above production method, at least one of the first conductive type layer and the second conductive type layer may be made from a non-single crystal body of an inorganic semiconductor, or at least one of an organic semiconductor and a conductive resin. With this configuration, there can be obtained an effect of easily forming at least one of the first conductive type layer and the second conductive type layer at a low temperature.
In the above production method, after formation of a first conductive type layer, the surface of the first conductive type layer may be oxidized or nitrided. With this configuration, there can be obtained an effect of easily forming an insulating film, thereby easily realizing the light emitting device of the present invention.
According to a fourth aspect of the present invention, there is provided a method of producing a light emitting device, including the steps of: forming a first conductive type cladding layer; forming a light emitting layer; forming an insulating layer; and forming a second conductive type cladding layer. With this configuration, there can be obtained an effect of easily producing the light emitting device of the present invention, thereby easily realizing the light emitting device of the present invention.
According to a fifth aspect of the present invention, there is provided a light emitting apparatus including: a plurality of light emitting devices stacked to each other. With this configuration, there can be obtained an effect of making pixels finer as compared with a light emitting apparatus in which a plurality of light emitting devices allowing light emission of different colors are disposed on a plane, thereby obtaining a high precision color display unit.
According to a sixth aspect of the present invention, there is provided a display unit including the light emitting device of the present invention. With this configuration, there can be obtained an effect of using a substrate made from an amorphous material such as glass, a plastic material, or a metal, thereby disposing a device array on a common substrate having a large area.